1. Technical Field of the Invention
This invention relates generally to heat exchangers for refrigerant circuits, and more particularly, to the heat exchange medium conducting elements which form a heat exchanging area of such heat exchangers.
2. Description of the Prior Art
Various types of heat exchangers are known in the prior art. For example, European Patent No. 0646759 A1, which is incorporated herein by reference, describes a laminated-type heat exchanger used in an evaporator of an automotive air conditioning refrigerant circuit, as shown in FIGS. 1-4. With reference to FIGS. 1-4, laminated-type evaporator 200 includes a plurality of tube units 201 of aluminum alloy that function as the heat exchange medium conducting elements and form a heat exchanging area 200a together with corrugated fins 20. Each of tube units 201 has a pair of tray-shaped plates 202 of a clad construction, whereby a brazing metal sheet is formed on a core metal.
Laminated-type evaporator 200 further includes a pair of parallel, closed-ended cylindrical pipes 230 and 240 positioned above the upper surface of laminated tube units 201. As shown in FIG. 2, cylindrical pipe 230 is positioned forward of cylindrical pipe 240 (to the right in FIG. 2). A plurality of substantially oval-shaped slots 231 are formed along the lower, curved surface of cylindrical pipe 230 at equal intervals. A plurality of substantially oval-shaped slots 241 also are formed along the lower, curved surface of cylindrical pipe 240 at equal intervals. Oval-shaped slots 231 of pipe 230 are aligned in parallel with substantially oval-shaped slots 241 of pipe 240, so as to receive a pair of tapered, hollow connecting portions 203b of tube units 201, which are described in detail below.
As illustrated in FIGS. 3A and 3B, each of tray-shaped plates 202 of tube unit 201 includes a depression 120 formed therein, a flange 13 formed around the periphery thereof, and wall 14 formed in the central region thereof. Wall 14 extends downwardly from an upper end of plate 202 and terminates about one-seventh of the length of plate 202 from the lower end thereof. Wall 14 includes a flat, top end portion 14a. A plurality of rectangular-shaped openings 14b, for example, five of such openings, as depicted in FIG. 3, are formed by punching at the flat, top end portion 14a of wall 14 along the length of wall 14 after the tray-shaped plate 202 is formed by press work.
Each of tray-shaped plates 202 has a pair of tapered, connecting tongues 203 projecting upwardly from the upper end thereof. One of the tongues 203 is disposed to the right of narrow wall 14, and the other tongue 203 is disposed to the left thereof A depression 203a is formed in the central region of tongue 203, and extends longitudinally from the upper end to the lower end thereof. Depression 203a is linked to depression 120 of plate 202. The bottom surface of depression 203a adjoins the plane of the inner bottom surface of depression 120.
With reference to FIGS. 3A-3B and 4, a plurality of annular cylindrical projections 16 and 17 project from the inner bottom surface of depression 120 and the bottom surface of depression 203a. Cylindrical projections 16 and 17 are formed, for example, by burring. Cylindrical projections 16 are located in depression 120 and depression 203a on the right side, i.e., forward, of wall 14, and cylindrical projections 17 are located on the left side, i.e., rearward, thereof. Cylindrical projections 16 are laterally aligned with one another at regular intervals in a plurality of rows. The rows of cylindrical projections 16 are arranged at regular intervals, but adjacent rows of cylindrical projections 16 are relatively offset from one another by about one half of the length of the interval between projections 16. Alternatively, cylindrical projections 16 may be arranged diagonally at regular intervals in a plurality of parallel, diagonal rows.
The arrangement of cylindrical projections 17 is similar to that of cylindrical projections 16. The arrangement of cylindrical projections 16 and 17 in one of the pair of plates 202 is identical to that in the other of the pair of plates 202, so that the pair of plates 202 may be joined.
Although cylindrical projections 16 and 17 are not depicted in the central region of shallow depression 120 in FIGS. 3A and 3B, cylindrical projections 16 and 17 may extend continuously along the length of shallow depression 120. As depicted in FIG. 4, an inner diameter D.sub.1 of each cylindrical projection 16 is greater than an outer diameter D.sub.2 of each cylindrical projection 17. In addition, an upper, end surface of each of cylindrical projections 16 and 17 extends over an upper surface of the flat, upper portion 14a of wall 14; the flat, upper end surface of each of tongues 203; and the plane of flange 13.
Evaporator 200 is temporarily assembled prior to the next sequential step of brazing in a manufacturing process thereof. When evaporator 200 is temporarily assembled, the pair of plates 202 are joined to each other by mating the plane of flanges 13; the flat, upper end surface of tongues 203; and an upper surface of the flat, upper end portions 14a of walls 14. When the pair of plates 202 are joined to each other, the upper end portions of cylindrical projections 17 are received in the upper end portions of the corresponding cylindrical projections 16, as shown in FIG. 4.
When the pair of tray-shaped plates 202 are joined together at flanges 13 so as to form a U-shaped passage 205 therebetween, the pair of tongues 203 of the pair of plates 202 define a pair of tapered, hollow connecting portions 203b. Walls 14 of each plate 202 contact one another at the upper surface of the flat, upper end portions 14a, thereby aligning the corresponding rectangular-shaped openings 14b with one another.
Heat exchanger area 200a of evaporator 200 is temporarily assembled by laminating together a plurality of tube units 201 and inserting corrugated fins 20 within intervening spaces 21, which are defined between adjacent tube units 201 by rectangular flanges 18. Rectangular flange 18 projects from the lower end of plate 202. Flange 18 projects downwardly from plate 202 and at substantially a right angle at the terminal end thereof. A pair of side plates 22 are attached to the left side of plate 202a, which is located on the rearward side of evaporator 200, and the right side of the plate 202b, which is located on the forward side of evaporator 200, respectively. Corrugated fins 20 are inserted within intervening spaces 21, which are defined between side plate 22 and plate 202a, and between side plate 22 and plate 202b, respectively, by means of rectangular flanges 22a. Rectangular flanges 22a project from the lower end of side plates 22 and are bent downwardly at substantially a right angle at the terminal end thereof. Although corrugated fins 20 are only depicted in FIG. 1 at the upper and lower ends of intervening spaces 21, corrugated fins 20 may extend continuously along the entire length of intervening spaces 21.
The pair of tapered, hollow connecting portions 203b of tube units 201 are inserted into slots 231 and 241 until the lower end portions of connecting portions 203b contact the inner peripheral surfaces of slots 231 and 241, respectively. Circular partition 234 is disposed at an intermediate location within the interior region of cylindrical pipe 230 so as to divide the cylindrical pipe 230 into a rearward section 230a and a forward side section 230b, as shown in FIG. 1. Thus, a process of temporarily assembling the evaporator 200 is completed.
After completion of the process of temporarily assembling evaporator 200, temporarily assembled evaporator 200 may be transported from an assembly line to a brazing furnace, so that elements constituting evaporator 200, such as tube units 201, cylindrical pipes 230 and 240, corrugated fins 20, side plates 22, and circular plate 234 may be fixedly connected to one another by means of brazing, for example, in an inert gas, e.g., helium, atmosphere.
In this process of brazing temporarily assembled evaporator 200, the mating surfaces of the pair of plates 202, such as flanges 13; the flat, upper end surface of each of tongues 203; the upper surface of the flat, upper end portion 14a of walls 14; and an upper inner and upper outer peripheral surface of the respective cylindrical projections 16 and 17 are brazed to one another, so as to fixedly join the pair of plates 202 to each other. In general, however, before the pair of plates 202 are fixedly joined to each other by brazing, aluminum oxide, which may have formed on the surfaces to be mated, is removed in order to more effectively join the pair of plates 202. For example, the surfaces to be mated are treated with flux to remove the aluminum oxide formed thereon.
According to this prior art embodiment, the flux is dissolved in water and sprayed on the entire exterior surface of the temporarily assembled pair of plates 202. Some of the flux solution applied to the exterior surface of the temporarily assembled pair of plates 202 seeps into small gaps between the mating surfaces of flanges 13 and the flat, upper end surfaces of tongues 203. Some of this flux solution also seeps into small air gaps created between the mating surface of the flat, upper end portion 14a of walls 14 through rectangular-shaped openings 14b. In addition, some of the flux solution applied to the exterior surface of the temporarily joined pair of plates 202 seeps between small radial air gaps created between an inner peripheral surface of the top end portion of cylindrical projections 16 and an outer peripheral surface of the top end portion of the corresponding cylindrical projections 17.
Thus, the flux solution seeps between substantially all of the mating surfaces of the temporarily assembled pair of plates 202. Therefore, substantially all of the entire mating surfaces of the temporarily joined pair of plates 202 to be brazed are effectively treated by the flux, so that aluminum oxide formed thereon is sufficiently removed before the mating surfaces of the pair of plates 202 are brazed to one another.
In the flux treatment method described above, water sprayed on the exterior surface of temporarily assembled evaporator 200 together with the flux is removed, for example, by natural vaporization, before temporarily assembled evaporator 200 is transported from the assembly line to the furnace in which the brazing process is performed.
According to this prior art heat exchanger, because only the exterior surface of the temporarily joined pair of plates 202 is covered with the flux, no residual flux collects on the inner bottom surface of depression 120 or the bottom surface of depression 203a. Therefore, the refrigerant flow path of the automotive air conditioning refrigerant circuit is not impeded by flakes of residual flux.
Moreover, in a separate brazing process, one end of inlet pipe 50 and one end of outlet pipe 60 are fixedly connected to circular openings 232 and 233, respectively, of cylindrical pipe 230 of FIG. 1. Circular openings 232 and 233 are formed at the rear and front end portions of cylindrical pipe 230, respectively, on the leading curved surface thereof. Inlet pipe 50 is provided with a union joint 50a at the other end thereof and outlet pipe 60 is similarly provided with a union joint 60a at the other end thereof.
As described above, after the operation of the press machine forming the tray-shaped plate 202 is completed, rectangular-shaped openings 14b may be formed at the flat, upper end portion 14a of wall 14 along the entire length of wall 14 by punching. Small rectangular scraps (not shown) are by products of the punching process. These scraps may interfere with further punching operation.
Specifically, when metal scraps remain on a mold (not shown) of a punching machine (not shown), small projections may form on an aluminum alloy material sheet due to the presence of such scraps on the mold. If the small projections are formed at the flat, upper end portion 14a of walls 14; the upper surfaces of flat, upper end portion 14a of walls 14 may not be in close contact with each other. As a result, the mating surfaces of walls 14 may not be effectively and sufficiently brazed, so that the inner pressure resistance of tube unit 201 is not be effectively increased. In addition, the presence of the scraps on the mold may cause damage to the mold.
In order to avoid the foregoing problems, a blower is sometimes used to blow away scraps punched from the walls 14 after every operation of the punching machine. However, a punching machine equipped with such a blower is mechanically complicated and expensive, thereby increasing the manufacturing cost of evaporator 200.